This invention relates in general to fire prevention systems and in particular to a spray system for aircraft cabins.
In August of 1985, a British Airtours Boeing 737 aborted its takeoff following an uncontained engine failure which pierced the wing fuel tanks and destroyed the fuselage. Tragically, heat and fumes overcame the fifty five passengers before they could evacuate the aircraft. Had the aircraft's cabin been equipped with a spray system, the passengers might have had enough time to escape.
A cabin spray system sprays a fine mist of water throughout the cabin or directly on the fire. The mist slows the spread of fire and reduces the heat and smoke in the cabin. A series of water tanks 2 are connected to center and outboard spray nozzles 4 and 6 distributed throughout the cabin 8 (see FIG. 1). The system is triggered either manually (e.g., by a member of the cabin crew) or automatically (e.g., by a thermal detection system). Once triggered, the system buys significant time for the passengers to evacuate the burning aircraft.
A relatively small amount of water is required. The amount depends upon duration that the system is required to operate, size of the aircraft, and other factors such as cabin air currents and temperature. Since most evacuations are completed within three and a half minutes, the system would have to operate for at least three minutes. According to an article entitled "Damping Down the Fires" in Flight International, a three minute discharge would require 270 liters of water for narrowbodies (e.g., Boeing 737) and 740 liters for widebodies (e.g., Airbus A300).
Even though used in small amounts, the water adds weight to the airframe. The extra weight, in turn, decreases fuel consumption, adding to the cost of operating the aircraft.
The aforementioned article suggests several ways in which the cost of storing water can be reduced. For example, the tanks can be eliminated by storing water instead of halon in cargo-hold fire-suppression systems. Or, the spray system could use ballast water stored in the airframe.
The article also mentions that the aircraft's potable, or drinkable, water supply can be used instead of dedicated tanks. However, the article advises against this approach because the water would be consumed during flight. Because roughly two-thirds of the accidents occur after takeoff, little water, if any, would be available to the cabin spray system at landing.
It is an object of this invention to reduce the cost of storing water for a cabin spray system.